Field of the Disclosure
The present disclosure relates to a display device, in which touch sensors are embedded in a pixel array.
Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices, and thus, can easily and comfortably control the electronic devices as they desire. Examples of a user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been essentially adopted in portable information devices, such as smart phones, and expanded to notebook computers, computer monitors, and home appliances. A technology (hereinafter referred to as “in-cell touch sensor technology”) has been recently proposed to embed touch sensors in a pixel array of a display panel. In the in-cell touch sensor technology, the touch sensors may be fabricated in the display panel without an increase in a thickness of the display panel. The touch sensors are connected to pixels through parasitic capacitances. In order to reduce a mutual influence attributable to coupling between the pixels and the touch sensors, one frame period may be time-divided into a period (hereinafter referred to as “display driving period”), in which the pixels are driven, and a period (hereinafter referred to as a “touch sensor driving period”), in which the touch sensors are driven.
In the in-cell touch sensor technology, electrodes connected to the pixels of the display panel are used as electrodes of the touch sensors. For example, in the in-cell touch sensor technology, a common electrode supplying a common voltage to pixels of a liquid crystal display is segmented, and segmented common electrode patterns are used as the electrodes of the touch sensors.
A parasitic capacitance connected to the in-cell touch sensors increases due to coupling between the in-cell touch sensors and the pixels. If the parasitic capacitance increases, touch sensitivity and accuracy of touch recognition may be deteriorated. A load free driving method is used to reduce an influence of the parasitic capacitance on the touch sensing.
The load free driving method supplies an AC (alternating current) signal having the same phase and the same amplitude as a touch driving signal to data lines and gate lines of the display panel during the touch sensor driving period, thereby reducing the influence of the parasitic capacitance between the touch sensors and the pixels on the touch sensing. More specifically, the load free driving method supplies a data voltage of an input image to the data lines and also supplies a gate pulse synchronized with the data voltage to the gate lines during the display driving period, and supplies the AC signal synchronized with the touch driving signal to the data lines and the gate lines during the touch sensor driving period.
In the load free driving method, because the touch driving signal and the AC signal having the same phase and the same amplitude are applied to both ends (the touch sensor and the signal lines) of the parasitic capacitance, the influence of the parasitic capacitance may be excluded. This is because voltages at both ends of the parasitic capacitance simultaneously change, and an amount of charges charged to the parasitic capacitance decreases as a voltage difference between both ends of the parasitic capacitance decreases. According to the load free driving method, an amount of charges charged to the parasitic capacitance is theoretically zero. Therefore, a load free effect recognized as if there is no parasitic capacitance may be obtained.
The load free effect may be obtained when the touch driving signal and the AC signal have completely the same phase and the same amplitude. However, a ripple is generated in the adjacent signal lines by the touch driving signal and the AC signal supplied to the signal lines during the touch sensor driving period.
The load free effect is reduced due to a noise resulting from the ripple generated by the touch driving signal and the AC signal.